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Abstract

The present invention relates to encoding and decoding of information using materials that are mildly absorbing radiation over a wide range of infrared wavelengths and substantially non-absorbing in the visible wavelengths. Examples of such encoding of information are bar codes and area markings. Information is encoded in markings on a base medium by depositing or intertexturing on the base medium a material where the surface dimensions, thickness and presence of the material contain the encoded information. The encoding utilizes a lower cost, more stable material than a material that is highly absorbing over a range of infrared wavelengths and substantially non-absorbing in the visible wavelengths. However, since the material is mildly absorbing in the infrared range, the signal obtained by reflecting or transmitting infrared radiation from the markings will be less distinct. Thus, inventive methods are needed to ensure that the encoded information can be decoded. Two different approaches are disclosed; (a) detecting the absorption spectrum and comparing to the known spectrum of the material in order to detect the presence and surface dimensions of the material and (b) utilizing techniques to improve the signal-to-noise such as restricting the range of wavelengths, matched filters and narrowing the bandwidth.

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First Claim